Synthesis and properties of zwitterionic phosphonioglycolates

Abstract Reaction of diphenylphosphane with glyoxylic acid hydrate in diethyl ether furnished diphenylphosphanylglycolic acid 1 and in a 1:2 molar ratio almost quantitatively the zwitterionic phosphonioglycolic acid glycolate 2 . Tertiary phosphanes with aryl or alkyl groups (phenyl, m/p -tolyl, p -anisyl, n -butyl, tert -butyl) react similarly to triorganylphosphonioglycolates 3a – h , which like 2 precipitate from the etheral solutions of the reactants. Tri- n -butylphosphonioglycolate ( 3e ) forms an ionic liquid and tri- tert -butylphosphonioglycolate ( 3f ) a viscous product whereas the other phosphonioglycolates are solids. Yields and stabilities of 3a – e increase with the P-basicity of the starting phosphane whereas bulky groups like tert -butyl cause destabilization. Compound 2 is the most stable phosphonioglycolate with only minor amounts of 1 in the solvolysis equilibrium in D 2 O. The triaryl and tributylphosphonioglycolates 3a – f decompose in protic solvents with recovery of tertiary phosphanes. On heating at 100 °C the compounds decompose to the corresponding phosphine oxides, minor amounts of glycolic acid and unidentified products.